1. Field of the Invention
The present invention relates to an optical disk recording method, a laser driving apparatus, and an optical disk apparatus for recording information by forming a recording mark on a recording medium whose physical properties are different from those of the other portions of the medium.
2. Description of the Related Art
There are various kinds of recordable optical disk media such as CD-R/RW, DVD-RAM, DVD±R/RW, Blu-ray Disc (hereinafter referred to as BD), HD DVD, and these media including one having two recording layers are in widespread use. Optical disk apparatuses supporting these media include the so-called DVD super multi-drive in widespread use which supports the recording/reproducing of CD-R/RW, DVD-RAM, and DVD±R/RW. It is expected that an ultimate super multi-drive having an additional function of supporting Blu-ray Disc and HD DVD will be developed.
In optical disk apparatuses, there is also an important technical problem of enhancing the recording speed. Nowadays, 52× CD, 16× DVD, and 2.4× BD drives are commercially produced. It is expected that a high-speed recording technology of BD and HD DVD will be a major technical problem in this field.
In conventional optical disks, recording marks are formed by intensity-modulated laser pulse trains, and there is mainly used a write strategy for compensating a start timing and an end timing of a laser pulse train in accordance with a recording mark length and the preceding and following space lengths. FIG. 2A shows a write strategy for 4.7 GB DVD-RAM shown in FIG. 1 of Japanese Unexamined Patent Application Publication No. 2003-187443. As shown in FIG. 2A, one recording mark is formed using a pulse train composed of a first pulse, an intermediate pulse, a last pulse, and a cooling pulse. There are used a total of four power values which are a power level for recording (peak power), a power level for erasing (bias power 1), a power level of the cooling pulse (bias power 2), and a power level of the bottom of the intermediate pulse (bias power 3).
As shown in FIG. 2B, a start timing Tsfp of a first pulse is determined in accordance with the preceding space length so and a recording mark length m1. An end timing Telp of a last pulse is determined in accordance with the recording mark length m1 and the following space length s1. These timings are called a 4×4 table-type strategy due to four divided mark lengths and space lengths. Further, Japanese Unexamined Patent Application Publication No. 5-234079 discloses a table-type write strategy that responds to further preceding mark lengths.
As for the high-speed recording technology of a BD write-once disk, Jpn. J. Appl. Phys. Vol. 45, (2006) pp. 1213-1218 reports the result of 12× recording/reproducing, which is the current maximum speed. It reports that basically a 4×4 table-type strategy has been used as the write strategy. Further, Proc. IOSM/ODS '05, TuP26, (2005) reports the recording result of 8× BD, which is the experiment result of high-speed recording next to the former.